Enum Impl

enum Impl {
    Preferred(PreferredRuntime),
    Dyn(Box<dyn DynProvider>),
}

Actual contents of a DynTimeProvider

We optimise the PreferredRuntime case. We could, instead, just use Box<dyn DynProvider> here.

The reason for doing it this way is that we expect this to be on many hot paths. Putting a message in a queue is extremely common, and we’d like to save a dyn dispatch, and reference to a further heap entry (which might be distant in the cache).

(Also, it’s nice to avoid boxing when we crate new types that use this, including our memory-quota-tracked mpsc streams, see tor-memquota::mq_queue.

The downside is that this means:

• This enum instead of a simple type
• The unsafe inside downcast_value.
• match statements in method shims

Variants

Preferred(PreferredRuntime)

Just (a handle to) the preferred runtime

Dyn(Box<dyn DynProvider>)

Some other runtime

Trait Implementations

impl Clone for Impl

fn clone(&self) -> Impl

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Impl

fn fmt(&self, formatter: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.